Development of an Antenna Emulator Device for the JuventasRadar Experiment on the HERA Mission

The Juventas Radar (JuRa), a monostatic radar system designed to probe Didymos binarysystem internal structure using a BPSK coded signal. A key component in ensuring the effectiveoperation of the JuRa system is the accurate matching of the dipole antenna impedance to thepower amplifier and receiver. In the transmitting path, the power amplifier performance is sensitiveto the loading impedance. For high efficient power amplifier this is a non-linear effect which ischallenging to model and simulate, especially for modulated signals. Calibration data obtained in astandard 50-ohm environment would be therfore inaccurate.Traditional deployment of antennas in an anechoic chamber for testing is not feasible due to the lowcenter frequency of 60 MHz as coupling with close objects and multiple reflections changeits frequency response. To address this challenge, we developed an antenna emulator device.The antenna emulator device is engineered to present an equivalent antenna-like impedancetowards the transmitter, mimicking the behavior of the actual antennas used in the JuRa systemwhen deployed in space. This device is crucial for testing and calibration because deploying actualantennas is impractical. Thus, the emulator provides a realistic impedance environment, ensuringthat the power amplifier operates under conditions that closely resemble those it will encounter inspace.Additionally, the emulator is equipped with input/output interfaces for monitoring TX signals andsignal injection for RX testing. However, these interfaces exhibit a inadvertently non-flat frequencyresponse, necessitating the development of a mathematical model to correct for these discrepanciesthrough post- and pre-processing techniques. The mathematical model developed for the emulator'sinput/output interfaces involves linear pre-and post-processing techniques, based on combination ofmultiple measurement of the antenna emulator device and instrument.The publication will detail the design process of the antenna emulator, including the theoreticalconsiderations and practical challenges (e.g. strong coupling with the solar panels) addressed duringits development. To facilitate testing during the assembly and integration (AIT) phases, wedeveloped a modified version of the emulator that can be used with non-deployed antennas. Thisversion allows for testing during the AIT without risking damaging the power amplifier by largevoltage standing wave ratio.Finally the principles and techniques developed for the Juventas Radar antenna emulator can beapplied to other missions with low-frequency antennas facing similar testing challenges. Byproviding a practical solution to the problem of testing low-frequency antennas withoutenvironmental interference, our approach offers a valuable tool for future planetary andinterplanetary space missions.